Investigating How Continental Geometry and Land Surface Properties Control Relative Humidity Over Land

Abstract:

Climate model simulations of warmer climates show strong decreases in relative humidity over land, which has important implications for future changes in heat stress and land habitability -- changes which have the potential to dramatically alter human comfort, activity, and productivity. Well-established theories exist for what sets changes in relative humidity over land in the tropics and subtropics, but these theories break down at midlatitudes. In particular, the influences of continental geometry and land surface properties on relative humidity at mid-latitudes are not well understood. We address these issues using an idealized atmospheric model coupled to a simple bucket land model. By varying the shape of a mid-latitude continent, the depth of the land bucket, and the “evaporative resistance” of the land, we are able to clarify the relationships between land surface properties and relative humidity over land. The simplicity of the model allows us to provide straightforward interpretations of the results, which can be applied to understand relative humidity changes in observations and climate models.